Current development of logging/measuring while drilling have enabled the development of new seismic tools that acquire and transmit seismic data in real time during the drilling process without impairing rig operations. This Seismic While Drilling (SWD) technology may significantly impact (positively) the cost of exploration and development drilling, particularly in deepwater environment and other areas with significant seismic uncertainties. The primary application of SWD is to locate the well properly in the seismic section so the driller can guide the well towards a target. SWD can further aid the driller with other drilling decisions including setting, coring, and casing points; drilling hazard avoidance; and overpressure zone identification.
In SWD, time-domain waveforms are captured by digitizing signal responses of a rock formation to an acoustic source at remote point relative to one or more microphones (e.g. hydrophones and/or geophones). Processors at the surface process the seismic time-domain data and translate it into a space-domain representation. In order to accomplish this, these processors employ a velocity model, which is usually estimated from the seismic data itself. However, the errors associated with these estimates can be quite large, especially in exploration areas where well information is scarce or non-existent. Such errors may result in the reflectors (and thus targets) being placed incorrectly in space. In order to properly place the well that is being drilled, either the seismic versus time profile or seismic versus depth profile is desired. Both of these can be achieved via SWD.
Seismic while drilling can potentially be done in at least three distinct ways: 1) using a downhole source (active or drill bit) and surface receivers; 2) using an active seismic source on the surface and one or more receivers downhole; 3) using both a downhole source and downhole receivers. The early commercial SWD services employed the first approach. However, with the advance of PDC bits, the drill bit signal was found in many situations to be too weak to serve as a useful seismic source.
The latter two options employ downhole receivers. Conventional drilling systems employ notoriously low-data-rate mud pulse telemetry systems to communicate downhole measurements to the surface. The bandwidth constraints of such systems make it infeasible to communicate all of the collected waveforms to the surface for processing, visualization, and interpretation. Previous attempts to address this issue are believed to be inadequate.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure, but on the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed with the given embodiments by the scope of the appended claims.